1. Field of the Invention
The present invention relates to a data processing apparatus, a data processing method and a data processing program, an encoding apparatus, an encoding method and an encoding program, and a decoding apparatus, a decoding method and a decoding program, respectively suitable for use in a case where video data is compression encoded by using orthogonal encoding and motion compensation by intra-picture prediction code.
2. Description of Related Art
In the fields of both information distribution by a broadcast station and the like and information reception by ordinary homes, an encoding apparatus and a decoding apparatus for image information are prevailing nowadays, the image information being in conformity with a compression coding method stipulated in MPEG (Moving Pictures Expert Group). The compression coding method deals with image information such as moving images as digital data, and by utilizing redundancy specific to image information, performs compression coding using orthogonal transformation such as discrete cosine transform and prediction coding using motion compensation.
An MEPEG2 standard in particular (Moving Pictures Experts Group 2: ISO (International Organization for Standardization)/IEC (International Electrotechnical Commission) 13818-2) is defined as a general image coding method. The MPEG 2 standard covers all of picture data by interlace scanning and picture data by progressive scanning as well as standard resolution pictures and high definition pictures, and is now widely used for a variety of applications for professional use and consumer use.
A high compression factor and a good picture quality can be achieved by utilizing the compression coding method of the MPEG2 standard, for example, by assigning an interlace scanning picture having a standard resolution of 720×480 pixels with a code amount of 4 to 8 Mbps (Bit per Second) as a bit rate, and an interlace scanning picture having a high resolution of 1920×1088 pixels with a code amount of 18 to 22 Mbps as a bit rate.
While the MPEG2 standard aimed at high image quality coding adaptive mainly to broadcasting use, it is not compatible with a coding method for a smaller code amount (low bit rate), i.e., a higher compression factor. Wide spread of portable terminals have increased a demand for a coding method capable of achieving a high compression factor and a low bit rate. To respond the remand, an MPEG4 standard has been developed. A standard called ISO/IEC 14496-2 was approved in December 1998 as an international standard for an image coding method.
Recently, international standardization of a moving image coding method called H.26L is under progress. H.26L was initially devised aiming at image coding for a television conference, and its target is to achieve a compression performance about twice that of the existing coding standard such as MPEG4.
As a part of activities of MPEG4, standardization basing upon H.26L, incorporating functions not supported by H.26L and achieving a higher coding efficiency, progresses presently in the form of Joint Model of Enhanced-Compression Video Coding. In March 2003, a coding method of an international standard was stipulated in ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) Recommendations H.264 or in ISO (International Organization for Standardization)/IEC (International Electrotechnical Commission) International Standard 14496-10 (MEPEG-4 part 10) Advanced Video Coding (hereinafter abbreviated to H.264|AVC). The content of processing on the basis of this stipulation is described in Non-Patent Document 1: “Draft Errata List with Revision-Marked Corrections for H.264/AVC”, JVT-1050, Thomas Wiegand et al., Joint Video Team (JVT) of ISO/IEC MPEG & ITU-T VCEG, 2003.
Coding techniques in compliance with the H.264|AVC specifications are described Japanese Unexamined Patent Application Publication No. 2006-25033 (Patent Document 1).
One of the features of a coding method in compliance with the H.264|AVC specifications is that a motion vector of a processing object is predicted by further using motion vectors of a block which is adjacent to or contacts the processing object block, in addition to a known coding method such as MPEG2 standard for achieving inter-frame compression by prediction coding utilizing orthogonal transformation and motion compensation. With reference to FIGS. 20A and 20B, coding utilizing prediction motion vector will be described briefly.
Encoding utilizing a prediction motion vector is performed in the unit of a macro block having a predetermined size and divided from a picture plane. It is herein assumed that the size of one macro block is 16×16 pixels. Encoding utilizing a prediction motion vector is performed from the macro block at the upper left corner in the picture plane, from the left end to right end in the picture plane, and from the upper end to lower end in the picture plane. Namely, an encoding process has already been completed for macro blocks at upper positions and left positions relative to a macro block to be processed.
As illustratively shown in FIG. 20A, a prediction motion vector PMV (E) of a processing object macro block E is obtained from medians of each of horizontal and vertical components of motion vectors MV(A), MV(B) and MV(C) of the macro block A left adjacent to the macro block E, the macro block B upper adjacent, and the macro block C upper right adjacent, respectively.